1. Field of the Invention
The present invention relates to novel polythioether/filler compositions in which the polythioether is a liquid which is curable at room temperature to form an elastomer having terminal groups which chemically bond to metallic surfaces such as aluminum alloy and aluminum composite surfaces, and/or to epoxy primer coatings applied to such surfaces. Such compositions are well suited for use in filling gaps, cracks or other narrow spaces in metallic, polymeric, composite and/or epoxy, polyurethane, or acrylic-primed surfaces since they are light in weight, they bond to such surfaces during curing at room temperatures as well as at elevated temperatures, they provide improved filler properties at very low temperatures, and they form smooth rubbery deposits having excellent water resistance and corrosion resistance, expansion-and-contraction properties and resistance to cracking.
2. Discussion of the Known Art
Reference is made to U.S. Pat. No. 4,366,307, the disclosure of which is incorporated by reference, for its disclosure of polythioether/filler compositions in which the polythioether is a liquid polymer which is curable at room temperature to form an elastomer having terminal vulcanizable or reactive groups such as silyl, hydroxy, alkoxy, mercapto and/or other reactive groups. The compositions of the Patent can contain amounts of filler, such as carbon-black, and are disclosed for use as water-, solvent-, fuel- and temperature-resistant sealants.
Various other polythioether liquid polymers are known which are curable at room temperatures to form rubbery solids which can contain fillers as colorants, conductivity particles, etc. While such compositions display better adhesive properties for metallic surfaces and better resistance to cracking than other gap-filling or caulking compositions, such as those based upon polyurethanes, silicone sealing polymers or other conventional binder materials used in caulking and gap-filling compositions, they present problems with respect to their use as binder materials for electroconductive fillers in gap-filler compositions.
Conventional polythioether/conductive filler compositions contain metallic powders, particles, or flakes, such as of nickel, to render the cured compositions electroconductive and heat-conductive. However, such metal particles, powders, and flakes render the gap-filler composition non-flowable or so slowly-flowable when used in the amounts necessary to impart sufficient conductivity, that the composition does not level when applied to cracks and gaps, such as over metal or composite surfaces, prior to solidification. This necessitates the additional step of sanding the gap or crack fill areas to render them level or coplanar with the surface areas.
In addition, the sanding of such composition is so hazardous to the health, due to the possible inhalation of the metal-containing dust, as to be prohibited by many safety regulatory agencies or to be permitted only with the use of masks or ventilation equipment.